The present invention relates to an apparatus for producing convex and/or concave spherical surfaces, and more particularly to an apparatus for producing optical lenses, such as one in which the workpiece, e.g. lens, to be machined is retained on the end face of a rotating spindle having angularly associated therewith a tool spindle on which the operating or grinding tool such as a cup wheel, is retained, with the relative angular disposition of the spindles being adjustable.
Apparatus for machining optical lenses are known in which a swivel arm is used to hold the tool spindle. A slider member acting as the mounting for such tool spindle is mounted in the usual way in a sliding guide on the swivel arm so as to be transversely displaceable relative thereto. The slider member is actuatable by means of an actuating spindle. This permits the operating or grinding tool, that is to say, the diamond cup wheel or disc usually employed for grinding optical lenses, to be adjusted accurately, within technical limitations, so that its cutting lip lies exactly, subject to such limitations, on the pivotal axis of the swivel arm.
Apart from the technical difficulties in manufacturing such a transverse slide mechanism for hold the tool spindle, the known arrangements have a major disadvantage in that spindle holders utilizing conventional sliding guides have inherent tolerances which cannot be completely removed or eliminated. Experience has shown that it is almost impossible, utilizing such devices, to obtain accurately pre-machined ground surfaces, such a lenses, which are capable of being polished.
For this reason, especially when producing optical lenses having a spherical surface, it has hitherto been necessary to carry out several separate operations such as pregrinding and precision grinding on different machines. In other words, to produce an at least substantially spherical surface on a workpiece, the workpiece must first be roughly prepared. To level off any remaining deviations or inaccuracies in the roughly prepared spherical surface with respect to sphericality and to reduce the degree of roughness so as to render the spherical surface polishable, it has been necessary for the workpiece to be subjected to further intermediate surface treatment using an accurately radially fixed tool on a precision grinding machine. Only after this additional machining operation is it possible, in a still further operation on a polishing machine, for the workpiece to be completed.
Hence, for a workpiece to be provided with a spherical surface, a number of treatment stages beginning with the rough grinding of the blank and ending with polishing of the spherical surface, which has been precision ground in an intermediate operation, were heretofore necessary. The number of treatment stages itself obviously has an adverse effect on the cost of manufacture of workpieces having a spherical surface. Moreover, the cost of providing a number of different processing machines, particularly the cost for producing or obtaining the accurately radially fixed precision grinding tools must be taken into account since, without these, a polishing operation in known radial grinding machines is impractical from a time factor aspect.
It is among the objects and advantages of the present invention to overcome the above noted deficiencies and disadvantages of the prior art and to provide an apparatus for producing polishable spherical surfaces in workpieces such as optical lenses, in a single operation while avoiding the use of radially fixed tools.
It is among the additional objects and advantages of the present invention to provide an apparatus which is structurally sound, readily monitorable and simple to operate.